1. Field
This document relates to a liquid crystal display in which an organic passivation film is partially removed from a pad area, and a method of fabricating the same.
2. Related Art
A high-resolution liquid crystal display uses an organic passivation film as its passivation film. The organic passivation film can reduce the parasitic capacitance of a display panel because it generally has a lower dielectric constant and is thicker compared to an inorganic passivation film.
In general, a pad area, as well as an active area, of a display panel where an image is displayed, is covered with the organic passivation film. In the active area, data lines and gate lines cross each other, and pixels are arranged in a matrix defined by a crossing structure of the data lines and the gate lines.
The pad area of the display panel may be divided into a first pad area to which output terminals of a drive IC (Integrated Circuit) are bonded, a second pad area to which input terminals of the drive IC are bonded, and a third pad area to which output terminals of an FPC (Flexible Printed Circuit) are bonded. Data pads are formed in the first pad area. The data pads are connected one-to-one to the data lines and bonded to the output terminals of the drive IC to transfer a data voltage output from the drive IC to the data lines. Pads formed in the third pad area are connected to ends of wires and bonded to the output terminals of the FPC. The wires are formed in a line pattern running across between the second pad area and the third pad area. The wires connect the input terminals of the drive IC and the output terminals of the FPC on a 1:2 basis. The same signal can be supplied to M (M is a positive integer equal to or greater than 1) through N output terminals (N is a positive integer equal to or greater than 1) of the FPC. In this case, the wires connect the input terminals of the drive IC and the output terminals of the FPC on an M:N basis.
The input/output terminals of the drive ICs and the output terminals of the FPCs are bonded to the pad area by an ACF (anisotropic conductive film). In an AFC bonding process, the ACF is placed on the pad area, a drive IC or FPC is aligned over the ACF, heat is applied to the ACF, and then the terminals of the drive IC or FPC are pressed against the ACF. Whether the bonding of the terminals of the drive IC or FPC and the pads is defective or not is determined based on the indentations formed in the pads. Since the terminals of the drive IC or FPC are pressed on the pads, with the ACF interposed between them, in the ACF bonding process, metal powder (or conductive balls) in the ACF forms indentations in the bonded parts of the data pads.
On the display panel where an organic passivation film is formed in the pad area, the organic passivation film PAC is partially removed from the pad area in order to open part of the pads, as shown in FIGS. 1 and 2. By the way, the organic passivation film PAC remaining in the pad area is formed thickly between the pads, and therefore no indentations, or only small indentations, if any, are formed after the driving IC bonding process. This makes it hard to ensure that the bonding between the pads and the terminals of the drive IC is done properly.
If no indentations, or only small indentations, if any, are formed, the bonding between the data pads and the drive IC or FPC is deemed defective and a repair process can be carried out. In the repair process, heat is applied to the pad area of the display panel and then the drive IC or FPC are pushed with a stick to separate the drive IC or FPC from the pad area of the display panel. However, when separating the drive IC or FPC from the pad area of the display panel in the repair process, a transparent electrode pattern formed on the pads or a metal pattern under it may be stripped off and lost. In this case, repair cannot be done, so the display panel should be discarded. The transparent electrode material may be ITO (Indium Tin Oxide).
FIG. 1 is a cross-sectional view showing a data pad to which a drive IC is bonded and an organic passivation film neighboring the data pad.
Referring to FIG. 1, the data pad comprises a gate metal pattern GM formed on a substrate SUBS and a transparent electrode pattern ITO formed over the gate metal pattern GM. A thick organic passivation film PAC is formed between pads. In FIG. 1, ‘GI’ is a gate insulating film formed on the substrate so as to cover the gate metal pattern GM. The gate metal pattern is connected to data lines of a display panel. ‘BPAS’ is a buffer passivation film made of an inorganic insulating material between the gate insulating film G1 and the organic passivation film PAC. ‘PAS’ is an upper passivation film made of an inorganic insulating material and covering the organic passivation film PAC. ‘DBUMP’ is an output terminal of the drive IC. The output terminal of the drive IC is brought into contact with the transparent electrode pattern ITO.
In the drive IC bonding process, if there is any misalignment at all between the output terminal DBUMP of the drive IC and the pad, no indentations or only small indentations, if any, are formed due to the thick organic passivation film PAC, and therefore the bonding is deemed defective. When separating the drive IC from the data pad during the repair process, the transparent electrode pattern ITO and the gate metal pattern GM may be stripped off and lost, as shown in FIG. 2. In this case, the display panel cannot be repaired and should be discarded.
A pad to which an output terminal of an FPC is bonded has a parallel structure that connects a gate metal pattern and a source-drain metal pattern, and can be formed in the output area of the FPC. If there is any misalignment at all between the output terminal of the FPC and the pad having the parallel structure, no indentations or only small indentations, if any, are formed due to the thick organic passivation film, and therefore the bonding is deemed defective. When separating the FPC from the pad having the parallel structure during the repair process, the gate metal pattern and the source-drain metal pattern may be stripped off and lost. In this case, the display panel cannot be repaired and should be discarded.